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<div class="titlepage"><div><div><h5 class="title">
<a name="spirit.karma.reference.operator.sequence"></a><a class="link" href="sequence.html" title="Sequence Generator (a &lt;&lt; b)">Sequence
          Generator (<code class="computeroutput"><span class="identifier">a</span> <span class="special">&lt;&lt;</span>
          <span class="identifier">b</span></code>)</a>
</h5></div></div></div>
<h6>
<a name="spirit.karma.reference.operator.sequence.h0"></a>
            <span class="phrase"><a name="spirit.karma.reference.operator.sequence.description"></a></span><a class="link" href="sequence.html#spirit.karma.reference.operator.sequence.description">Description</a>
          </h6>
<p>
            Generator sequences are used to consecutively combine different, more
            primitive generators. All generators in a sequence are invoked from left
            to right as long as they succeed.
          </p>
<h6>
<a name="spirit.karma.reference.operator.sequence.h1"></a>
            <span class="phrase"><a name="spirit.karma.reference.operator.sequence.header"></a></span><a class="link" href="sequence.html#spirit.karma.reference.operator.sequence.header">Header</a>
          </h6>
<pre class="programlisting"><span class="comment">// forwards to &lt;boost/spirit/home/karma/operator/sequence.hpp&gt;</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">spirit</span><span class="special">/</span><span class="identifier">include</span><span class="special">/</span><span class="identifier">karma_sequence</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
</pre>
<p>
            Also, see <a class="link" href="../../../structure/include.html" title="Include">Include Structure</a>.
          </p>
<h6>
<a name="spirit.karma.reference.operator.sequence.h2"></a>
            <span class="phrase"><a name="spirit.karma.reference.operator.sequence.model_of"></a></span><a class="link" href="sequence.html#spirit.karma.reference.operator.sequence.model_of">Model of</a>
          </h6>
<div class="blockquote"><blockquote class="blockquote"><p>
              <a class="link" href="../generator_concepts/narygenerator.html" title="NaryGenerator"><code class="computeroutput"><span class="identifier">NaryGenerator</span></code></a>
            </p></blockquote></div>
<h6>
<a name="spirit.karma.reference.operator.sequence.h3"></a>
            <span class="phrase"><a name="spirit.karma.reference.operator.sequence.expression_semantics"></a></span><a class="link" href="sequence.html#spirit.karma.reference.operator.sequence.expression_semantics">Expression
            Semantics</a>
          </h6>
<p>
            Semantics of an expression is defined only where it differs from, or
            is not defined in <a class="link" href="../generator_concepts/narygenerator.html" title="NaryGenerator"><code class="computeroutput"><span class="identifier">NaryGenerator</span></code></a>.
          </p>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>
                    <p>
                      Expression
                    </p>
                  </th>
<th>
                    <p>
                      Semantics
                    </p>
                  </th>
</tr></thead>
<tbody><tr>
<td>
                    <p>
                      <code class="computeroutput"><span class="identifier">a</span> <span class="special">&lt;&lt;</span>
                      <span class="identifier">b</span></code>
                    </p>
                  </td>
<td>
                    <p>
                      The generators <code class="computeroutput"><span class="identifier">a</span></code>
                      and <code class="computeroutput"><span class="identifier">b</span></code> are executed
                      sequentially from left to right and as long as they succeed.
                      A failed generator stops the execution of the entire sequence
                      and makes the sequence fail as well.
                    </p>
                  </td>
</tr></tbody>
</table></div>
<p>
            It is important to note, that sequences don't perform any buffering of
            the output generated by its elements. That means that any failing sequence
            might have already generated some output, which is <span class="emphasis"><em>not</em></span>
            rolled back.
          </p>
<div class="tip"><table border="0" summary="Tip">
<tr>
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Tip]" src="../../../../images/tip.png"></td>
<th align="left">Tip</th>
</tr>
<tr><td align="left" valign="top">
<p>
              The simplest way to force a sequence to behave as if it did buffering
              is to wrap it into a buffering directive (see <a class="link" href="../directive/buffer.html" title="Generator Directive for Temporary Output Buffering (buffer[])"><code class="computeroutput"><span class="identifier">buffer</span></code></a>):
            </p>
<p>
</p>
<pre class="programlisting"><span class="identifier">buffer</span><span class="special">[</span><span class="identifier">a</span> <span class="special">&lt;&lt;</span> <span class="identifier">b</span> <span class="special">&lt;&lt;</span> <span class="identifier">c</span><span class="special">]</span></pre>
<p>
            </p>
<p>
              which will <span class="emphasis"><em>not</em></span> generate any output in case of
              a failing sequence.
            </p>
</td></tr>
</table></div>
<h6>
<a name="spirit.karma.reference.operator.sequence.h4"></a>
            <span class="phrase"><a name="spirit.karma.reference.operator.sequence.attributes"></a></span><a class="link" href="sequence.html#spirit.karma.reference.operator.sequence.attributes">Attributes</a>
          </h6>
<p>
            See <a class="link" href="../../quick_reference/compound_attribute_rules.html#spirit.karma.quick_reference.compound_attribute_rules.notation">Compound
            Attribute Notation</a>.
          </p>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>
                    <p>
                      Expression
                    </p>
                  </th>
<th>
                    <p>
                      Attribute
                    </p>
                  </th>
</tr></thead>
<tbody><tr>
<td>
                    <p>
                      <code class="computeroutput"><span class="identifier">a</span> <span class="special">&lt;&lt;</span>
                      <span class="identifier">b</span></code> (sequence)
                    </p>
                  </td>
<td>
                    <p>
</p>
<pre xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="table-programlisting"><span class="identifier">a</span><span class="special">:</span> <span class="identifier">A</span><span class="special">,</span> <span class="identifier">b</span><span class="special">:</span> <span class="identifier">B</span> <span class="special">--&gt;</span> <span class="special">(</span><span class="identifier">a</span> <span class="special">&lt;&lt;</span> <span class="identifier">b</span><span class="special">):</span> <span class="identifier">tuple</span><span class="special">&lt;</span><span class="identifier">A</span><span class="special">,</span> <span class="identifier">B</span><span class="special">&gt;</span>
<span class="identifier">a</span><span class="special">:</span> <span class="identifier">A</span><span class="special">,</span> <span class="identifier">b</span><span class="special">:</span> <span class="identifier">Unused</span> <span class="special">--&gt;</span> <span class="special">(</span><span class="identifier">a</span> <span class="special">&lt;&lt;</span> <span class="identifier">b</span><span class="special">):</span> <span class="identifier">A</span>
<span class="identifier">a</span><span class="special">:</span> <span class="identifier">Unused</span><span class="special">,</span> <span class="identifier">b</span><span class="special">:</span> <span class="identifier">B</span> <span class="special">--&gt;</span> <span class="special">(</span><span class="identifier">a</span> <span class="special">&lt;&lt;</span> <span class="identifier">b</span><span class="special">):</span> <span class="identifier">B</span>
<span class="identifier">a</span><span class="special">:</span> <span class="identifier">Unused</span><span class="special">,</span> <span class="identifier">b</span><span class="special">:</span> <span class="identifier">Unused</span> <span class="special">--&gt;</span> <span class="special">(</span><span class="identifier">a</span> <span class="special">&lt;&lt;</span> <span class="identifier">b</span><span class="special">):</span> <span class="identifier">Unused</span>

<span class="identifier">a</span><span class="special">:</span> <span class="identifier">A</span><span class="special">,</span> <span class="identifier">b</span><span class="special">:</span> <span class="identifier">A</span> <span class="special">--&gt;</span> <span class="special">(</span><span class="identifier">a</span> <span class="special">&lt;&lt;</span> <span class="identifier">b</span><span class="special">):</span> <span class="identifier">vector</span><span class="special">&lt;</span><span class="identifier">A</span><span class="special">&gt;</span>
<span class="identifier">a</span><span class="special">:</span> <span class="identifier">vector</span><span class="special">&lt;</span><span class="identifier">A</span><span class="special">&gt;,</span> <span class="identifier">b</span><span class="special">:</span> <span class="identifier">A</span> <span class="special">--&gt;</span> <span class="special">(</span><span class="identifier">a</span> <span class="special">&lt;&lt;</span> <span class="identifier">b</span><span class="special">):</span> <span class="identifier">vector</span><span class="special">&lt;</span><span class="identifier">A</span><span class="special">&gt;</span>
<span class="identifier">a</span><span class="special">:</span> <span class="identifier">A</span><span class="special">,</span> <span class="identifier">b</span><span class="special">:</span> <span class="identifier">vector</span><span class="special">&lt;</span><span class="identifier">A</span><span class="special">&gt;</span> <span class="special">--&gt;</span> <span class="special">(</span><span class="identifier">a</span> <span class="special">&lt;&lt;</span> <span class="identifier">b</span><span class="special">):</span> <span class="identifier">vector</span><span class="special">&lt;</span><span class="identifier">A</span><span class="special">&gt;</span>
<span class="identifier">a</span><span class="special">:</span> <span class="identifier">vector</span><span class="special">&lt;</span><span class="identifier">A</span><span class="special">&gt;,</span> <span class="identifier">b</span><span class="special">:</span> <span class="identifier">vector</span><span class="special">&lt;</span><span class="identifier">A</span><span class="special">&gt;</span> <span class="special">--&gt;</span> <span class="special">(</span><span class="identifier">a</span> <span class="special">&lt;&lt;</span> <span class="identifier">b</span><span class="special">):</span> <span class="identifier">vector</span><span class="special">&lt;</span><span class="identifier">A</span><span class="special">&gt;</span></pre>
<p>
                    </p>
                  </td>
</tr></tbody>
</table></div>
<div class="important"><table border="0" summary="Important">
<tr>
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Important]" src="../../../../images/important.png"></td>
<th align="left">Important</th>
</tr>
<tr><td align="left" valign="top">
<p>
              The table above uses <code class="computeroutput"><span class="identifier">tuple</span><span class="special">&lt;</span><span class="identifier">A</span><span class="special">,</span> <span class="identifier">B</span><span class="special">&gt;</span></code> and <code class="computeroutput"><span class="identifier">vector</span><span class="special">&lt;</span><span class="identifier">A</span><span class="special">&gt;</span></code> as placeholders only.
            </p>
<p>
              The notation <code class="computeroutput"><span class="identifier">tuple</span><span class="special">&lt;</span><span class="identifier">A</span><span class="special">,</span> <span class="identifier">B</span><span class="special">&gt;</span></code> stands for <span class="emphasis"><em>any fusion
              sequence of two elements</em></span>, where <code class="computeroutput"><span class="identifier">A</span></code>
              is the type of its first element and <code class="computeroutput"><span class="identifier">B</span></code>
              is the type of its second element.
            </p>
<p>
              The notation of <code class="computeroutput"><span class="identifier">vector</span><span class="special">&lt;</span><span class="identifier">A</span><span class="special">&gt;</span></code> stands for <span class="emphasis"><em>any STL container</em></span>
              holding elements of type <code class="computeroutput"><span class="identifier">A</span></code>.
            </p>
</td></tr>
</table></div>
<p>
            The attribute composition and propagation rules as shown in the table
            above make sequences somewhat special as they can operate in two modes
            if all elements have the same attribute type: consuming fusion sequences
            and consuming STL containers. The selected mode depends on the type of
            the attribute supplied.
          </p>
<h6>
<a name="spirit.karma.reference.operator.sequence.h5"></a>
            <span class="phrase"><a name="spirit.karma.reference.operator.sequence.complexity"></a></span><a class="link" href="sequence.html#spirit.karma.reference.operator.sequence.complexity">Complexity</a>
          </h6>
<div class="blockquote"><blockquote class="blockquote"><p>
              The overall complexity of the sequence generator is defined by the
              sum of the complexities of its elements. The complexity of the sequence
              itself is O(N), where N is the number of elements in the sequence.
            </p></blockquote></div>
<h6>
<a name="spirit.karma.reference.operator.sequence.h6"></a>
            <span class="phrase"><a name="spirit.karma.reference.operator.sequence.example"></a></span><a class="link" href="sequence.html#spirit.karma.reference.operator.sequence.example">Example</a>
          </h6>
<div class="note"><table border="0" summary="Note">
<tr>
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../images/note.png"></td>
<th align="left">Note</th>
</tr>
<tr><td align="left" valign="top"><p>
              The test harness for the example(s) below is presented in the <a class="link" href="../basics.html#spirit.karma.reference.basics.examples">Basics Examples</a>
              section.
            </p></td></tr>
</table></div>
<p>
            Some includes:
          </p>
<p>
</p>
<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">spirit</span><span class="special">/</span><span class="identifier">include</span><span class="special">/</span><span class="identifier">karma</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">spirit</span><span class="special">/</span><span class="identifier">include</span><span class="special">/</span><span class="identifier">support_utree</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">phoenix</span><span class="special">/</span><span class="identifier">core</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">phoenix</span><span class="special">/</span><span class="keyword">operator</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">fusion</span><span class="special">/</span><span class="identifier">include</span><span class="special">/</span><span class="identifier">std_pair</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">proto</span><span class="special">/</span><span class="identifier">deep_copy</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">iostream</span><span class="special">&gt;</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">string</span><span class="special">&gt;</span>
</pre>
<p>
          </p>
<p>
            Some using declarations:
          </p>
<p>
</p>
<pre class="programlisting"><span class="keyword">using</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">karma</span><span class="special">::</span><span class="identifier">double_</span><span class="special">;</span>
</pre>
<p>
          </p>
<p>
            Basic usage of a sequence:
          </p>
<p>
</p>
<pre class="programlisting"><span class="identifier">test_generator_attr</span><span class="special">(</span><span class="string">"1.0,2.0"</span><span class="special">,</span> <span class="identifier">double_</span> <span class="special">&lt;&lt;</span> <span class="char">','</span> <span class="special">&lt;&lt;</span> <span class="identifier">double_</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">make_pair</span><span class="special">(</span><span class="number">1.0</span><span class="special">,</span> <span class="number">2.0</span><span class="special">));</span>
</pre>
<p>
          </p>
</div>
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<td align="right"><div class="copyright-footer">Copyright © 2001-2011 Joel de Guzman, Hartmut Kaiser<p>
        Distributed under the Boost Software License, Version 1.0. (See accompanying
        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
      </p>
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